Starfish can use eyes at the tips of their arms to find their way home.

Credit: DAN-ERIC NILSSON

Most sea-star species have compound eyes on their arms, but there has been no direct evidence that the eyes enable vision. In field experiments, Anders Garm at the University of Copenhagen and Dan-Eric Nilsson at Lund University in Sweden displaced blue starfish (Linckia laevigata) from the coral reefs they inhabit off the coast of Japan. The starfish were able to navigate their way back to the reef from distances of up to two metres, an ability that was lost when the researchers surgically removed the animals' eyes.

The distribution and shape of the eyes (pictured) and the arrangement of their light- sensing cells suggest that the starfish can recognize the reef from only relatively short distances. This might help the creatures to stay close to home, the researchers say.

Proc. R. Soc. B 281, 20133011 (2014)